1. Field of the Invention
The present invention relates, in general, to a quasicrystalline phase-reinforced Mg-based metallic alloy superior in warm and hot formability and, more particularly, to an Mgxe2x80x94Znxe2x80x94Y alloy which has a two-phase region consisting of a quasicrystalline phase and a magnesium-based solid solution phase, in which the solid solution is formed as a primary phase constituting a matrix structure upon solidification, while the quasicrystalline phase serves as a second phase and forms, together with the solid solution phase, a eutectic phase, thereby reinforcing the matrix.
2. Description of the Prior Art
Casings for portable electronic appliances, such as mobile phones, or materials for automobile parts are required to be of light weight, high strength, high toughness, and high formability.
While crystals generally have one-, two-, three-, and six-fold rotational axes of symmetry only, quasicrystals have five-, eight-, ten- and twelve-fold rotational axes of symmetry, which are not formed in crystals. Since their first finding in Alxe2x80x94Mn alloy, quasicrystals have been disclosed to exist in many alloys. For instance, Alxe2x80x94Cuxe2x80x94Fe, Mgxe2x80x94Znxe2x80x94Y, and Alxe2x80x94Pdxe2x80x94Mn alloys have been reported to have thermodynamically stable quasicrystalline structures. Superior as they are in hardness as compared to crystals of similar compositions, quasicrystals are unsuitable for use as sole structural materials owing to their high brittleness. Recently, reinforced composite materials which comprise metal matrices having reinforcement particles dispersed in the matrix have been developed through powder metallurgy route.
U.S. Pat. No. 5,851,317 discloses composite materials reinforced with quasicrystalline particles and a gas atomization process of making the same, in which aluminum or aluminum alloy particles and spherical Alxe2x80x94Cuxe2x80x94Fe quasicrystalline particles are mixed at an appropriate ratio and hot pressed or hot extruded to form a composite product of high strength with interfacial bonding between the quasicrystalline particles and the aluminum or aluminum alloy particles.
The composite materials of the cited reference have the advantage of being made to show versatile mechanical properties by controlling the amounts of components, but the disadvantage of being poor in bonding strength between component particles. In case particles that are likely to be coated with oxides, such as aluminum or aluminum alloy particles, are used as starting materials, the oxide coatings deteriorate the bonding between the matrix metal particles and the reinforcement particles, giving rise to a decrease in mechanical properties, especially elongation and fracture toughness. Additionally, the composite materials are not advantageous in terms of product reliability and production cost owing to their complicated production procedure and many production parameters.
Further, Alxe2x80x94Cuxe2x80x94Fe alloy is unsuitable as materials for use in casings for electronic appliances or materials for automobile parts, which require lightness, high strength, high toughness and high formability because the quasicrystalline phase region in Alxe2x80x94Cuxe2x80x94Fe alloy is surrounded by various brittle intermetallic phase regions.
Therefore, there remains a need for the alloy that has a quasicrystalline phase as a second phase dispersed in the metal solution so that it is provided with all of the above mechanical properties in addition to being of high formability.
Leading to the present invention, the intensive and thorough research on metallic alloy, conducted by the present inventors, resulted in the finding that, when Mgxe2x80x94Znxe2x80x94Y alloy is solidified from a liquid state, the quasicrystalline phase particles in the matrix of the metal solid solution acts as a reinforcement, which brings about an improvement in the mechanical properties of quasicrystalline phase-reinforced materials and their production cost. In the present invention, the Mgxe2x80x94Znxe2x80x94Y alloy is defined as the composition range which allows hot molding processes to be applied to the alloy.
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a quasicrystalline phase-reinforced magnesium-based metallic alloy with excellent warm and hot formability, in which a two-phase region consisting of a quasicrystalline phase and a magnesium-based solid solution phase exists, said magnesium-based solid solution phase (alpha magnesium) being formed as a primary solid phase, constituting a matrix structure upon being solidified, said quasicrystalline phase serving as a second phase and forming, together with the magnesium-based solid solution phase, a eutectic phase, thereby reinforcing the matrix.
It is another object of the present invention to provide a method of making such an quasicrystalline phase-reinforced magnesium-based metallic alloy by subjecting a magnesium-based metallic alloy composition to hot forming to separate and disperse a quasicrystalline phase of micro particles throughout the metallic matrix, so as to bring about an improvement in room temperature mechanical properties as well as high-temperature elongation.